Fastening device

ABSTRACT

A fasting device has a shaft and a clamping assembling. The clamping assembly has an outer housing shaped so as to retain the object to be clamped in position and an inner core rotatably disposed within the outer housing and in threaded engagement with a hole in one of the outer housing. A sprag is disposed within the outer housing and located in a slot in the inner core, both the inner core and the sprag plate having through holes to receive the shaft. A bias spring biases the sprag into engagement with the inner core.

BACKGROUND OF THE INVENTION

This invention relates to a fastening device, and more particularly, toa device for fastening a spare wheel on to a vehicle.

A number of problems arise when fastening the spare wheel of a vehicleinto its storage position. It is advantageous to have a fixing mechanismfor the wheel which is simple to operate as well as being quickly andeasily detachable. At the same time, however, the device must providesufficient fastening strength to prevent it from working loose due tothe vibrations and the shocks received during normal operation. Inaddition, as the thickness of the hub of the spare wheel can varyaccording to wheel type, it is advantageous to provide a fastening whichprovides adequate clamping load independent of wheel hub thickness.

SUMMARY OF THE INVENTION

According to the present invention there is provided a fastening devicecomprising a shaft and a clamping assembly, the clamping assemblyhaving:

an outer housing shaped so to as retain the object to be clamped inposition; an inner core rotatably disposed within the outer housing andin threaded engagement with a hole in one end of the outer housing; asprag plate disposed within the outer housing and located in a slot inthe inner core, both the inner core and the sprag plate having throughholes to receive the shaft, and a bias spring for biasing the spragplate in to engagement with the inner core, the arrangement being suchthat when the inner core is rotated in relation to the outer housing thesprag plate pivots between a first position normal to the shaft, inwhich the shaft is free to move through the hole in the sprag plate, anda second position inclined relative to the shaft, in which the shaft isgripped by the sprag plate.

The shaft may be smooth or, alternatively, may be screw-threaded orannularly ribbed.

The shaft may be of non-circular cross section, and engageable with ahole of similar cross-section through the inner core of the clampingassembly, so that, when the clamping assembly is in engagement with theshaft, rotation of the outer housing causes pivoting of the sprag plateand fastens the clamping assembly to the shaft.

The shaft may be fixed to the vehicle and the clamping assemblyremovable from it or, alternatively, the shaft may be fixed to theclamping assembly and spring loaded to eject when the sprag is released,the shaft having a "T" shaped end connectable with a support fixed tothe vehicle so that an initial turn of the inner core locates and locksthe shaft, and a further turn of the inner core engages the sprag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional perspective view of the fastening devicehaving a threaded shaft.

FIG. 2 is a cross-sectional perspective view of the fastening devicehaving a smooth shaft.

FIG. 3 is a cross-sectional perspective view of the fastening devicehaving an annularly-ribbed shaft.

FIG. 4 is a cross-sectional perspective view of the fastening devicehaving a non-circular shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One example of the present invention will now be described withreference to FIG. 1 which is a sectional view of the fixing device.

The fastening device has a right-handed screw threaded shaft 1 and aclamping assembly 2. The clamping assembly 2 has a hole 3 through itscentre, large enough to allow the shaft 1 to pass through it.

The clamping assembly 2 has an outer housing 5 in threaded engagementwith an inner core 6, the housing 5 and the core 6 being arranged sothat the core 6 is rotatable in relation to the housing 5. Disposedwithin the housing 5 and located within a slot 13 in the core 6 is asprag plate 9. The sprag plate 9 is urged into engagement with a side 14of the slot 13 by a helical bias spring 12. 0n one edge of the side 14of the slot 13 is a raised lip 11, so that the sprag plate 9 restsinclined to the axis of the hole 3.

In use a spare wheel, not shown in the drawings, is placed over thescrew-threaded shaft 1. The clamping assembly 2 is then placed on to theshaft 1 with the shaft 1 passing through the hole 3. The clampingassembly 2 is then pushed toward the base of the shaft 1, so that thewheel is clamped firmly between the base of the slot and the outer rim 4of the outer housing 5 of the clamping assembly 2. In this position, thecore 6 is screwed fully onto the housing 5 and the sprag plate abuts theinternal end face 10 of the housing 5.

Whilst holding the outer housing 5 (or due to it being held by frictionwith the wheel hub), the inner core 6 is rotated clockwise causing theinner core 6 to move away from the base of the shaft 1 due to theleft-handed threaded engagement 8 of the outer housing 5 and the innercore 6. One edge of the sprag plate 9 then comes out of engagement withthe inner face 10 of the outer housing 5. Continued rotation of theinner core 6 causes the sprag plate 9 to pivot further and clamp on tothe shaft 1. The wheel is then held firm.

To release the wheel, the inner core 6 is rotated in the oppositedirection, causing the sprag 9 to pivot and eventually release the shaft1.

Alternative embodiments of the present invention are shown in FIGS. 2, 3and 4. The shaft may be smooth (i.e., shaft 1' shown in FIG. 2) orannularly fibbed (shaft 1" shown in FIG. 3). As shown in FIG. 4, theshaft may also be of non-circular cross-section (i.e., shaft 1'") andengageable with a hole of similar cross-section (i.e., hole 3'") throughthe inner core of the clamping assembly.

What is claimed is:
 1. A fastening device comprising a shaft (1) and a clamping assembly (2), the clamping assembly having:an outer housing (5) shaped so as to retain an object to be clamped in position; an inner core (6) rotatably disposed within the outer housing and in threaded engagement with a hole in one end of the outer housing; a sprag plate (9) disposed within the outer housing and located in a slot (13) in the inner core, both the inner core and the sprag plate having through holes (3) to receive the shaft, and a bias spring (2) for biasing the sprag plate into engagement with the inner core, such that when the inner core is rotated in relation to the outer housing the sprag plate pivots between a first position normal to the shaft, in which the shaft is free to move through the hole in the sprag plate, and a second position inclined relative to the shaft, in which the shaft is gripped by the sprag plate.
 2. A fastening device according to claim 1, wherein the shaft (1) is smooth.
 3. A fastening device according to claim 1, wherein the shaft (1) is screw-threaded.
 4. A fastening device according to claim 1, wherein the shaft (1) is annularly ribbed.
 5. A fastening device according to claim 1, wherein the shaft (1) is of non-circular cross section, and is engageable with the through holes, the through holes having a similar cross-section through the inner core (6) of the clamping assembly (2), so that, when the clamping assembly is in engagement with the shaft, rotation of the outer housing (5) causes pivoting of the sprag plate (9) and fastens the clamping assembly to the shaft.
 6. A fastening device according to claim 1, wherein the shaft (1) is, adapted to be fixed to a vehicle and the clamping assembly (2) removable from the shaft. 